Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/39—Preparation of carboxylic acid esters by oxidation of groups which are precursors for the acid moiety of the ester
  • C07C67/40—Preparation of carboxylic acid esters by oxidation of groups which are precursors for the acid moiety of the ester by oxidation of primary alcohols

Definitions

• This invention relates to a process for preparing esters directly from alcohols. More particularly, this invention relates to a process for preparing esters by reacting alcohols which are substituted on the 2-carbon position whereby dehydrogenation and esterification occur using certain catalysts.
• Guerbet alcohols which are branched dimerized or condensed alcohols resulting from the condensation of a primary alcohol or a mixture of primary alcohols. Such alcohols are characterized as containing branching in the 2-carbon position, which is the carbon atom adjacent to the hydroxyl carbon.
• di-(tridecyl)tridecanoate can also be formed through oxidation of the starting alcohol to an acid and subsequent esterification with the di- alcohol product.
• Example 1 of Miller et al. reports the formation of the di-(tridecyl)tridecanoate product, which is a 39-carbon atom ester product.
• the present invention is based on the discovery that Guerbet alcohols can be used to form esters directly in a dehydrogenation-esterification reaction using certain catalysts and temperatures and at high selectivities and conversions.
• % platinum on a high surface area activated carbon support 0.4 wt% to 10 wt% zinc oxide or 0.05 wt% to 5 wt% zinc in the form of an alcohol-soluble zinc carboxylate having 2 to 20 carbon atoms and (b) at least about 0.2 wt. % NaOH, KOH or LiOH, said percentages of said catalyst components being based on the amount of alcohol in the reaction mixture.
• the process of this invention is therefore a convenient and effective method for providing long chain esters of alcohols such as 2-ethylhexanol and the Guerbet condensate of oxo-isooctanol, which condensate is a C16 alcohol.
• the preferred alcohols which are subjected to the ester-forming process of this invention are 2-substituted alcohols of the formula: where R1 is a straight or branched chain alkyl having 3 to 20 carbon atoms and R2 is a straight or branched alkyl having 2 to 18 carbon atoms.
• Such alcohols are those which result from the Guerbet condensation of two primary alcohols.
• the process of this invention is conducted at a temperature of about 170°C to 240°C and preferably at a temperature of about 185°C to about 200°C.
• the reaction is effected by adding the catalyst components to the alcohol or alcohols to be reacted and heating the mixture to the desired temperature while removing water and hydrogen which are formed as the reaction proceeds. Reaction times are typically about 2 to 5 hours. Conversions to the ester product have been obtained in the range of about 20 to 75%.
• the catalyst system found effective in the present invention comprises two components.
• the first of these may be (i) platinum dispersed on high surface area activated carbon, (ii) zinc oxide, or (iii) an alcohol-soluble zinc carboxylate salt of a carboxylic acid having 2 to 20 carbon atoms.
• the preferred catalysts of the first component are platinum on activated carbon wherein 5 wt. % platinum based on the weight of the carbon is present and zinc carboxy­lates having about 6 to 20 carbon atoms, such as zinc stearate or the zinc salts of neo-acids (acids having a tertiary carbon atom) such as neo-decanoic acid.
• platinum When platinum is used, it is present in an amount of from at least about 0.0024 wt. % platinum up to about 0.1 wt. % platinum, preferably about 0.005 to about 0.008 wt. % platinum being present.
• the platinum/activated carbon catalyst should have a surface area of at least 500 M2/g. and a particle size of less than 200 microns. Preferably it has a surface area of about 1000 to 1200 M2/g. (square meters per gram) and a mean particle size of less than 100 microns, such as about 30 microns, with 90% by weight of the activated carbon particles have a particle size less than 70 microns.
• the amount of platinum dispersed onto the activated carbon may vary from about 1 to 10 wt. % based on the total weight of activated carbon and platinum.
• Zinc carboxylate when present, is used in an amount of from about 0.05 wt. % zinc up to about 5 wt. % zinc, and preferably about 0.1 to 0.3 wt. % zinc is used (present in the form of zinc carboxylate).
• the amounts may vary from about 0.4 wt. % to about 10 wt. %, with the preferred range being from about 1 to 3 wt. %.
• the second component of the catalyst may be sodium hydroxide, potassium hydroxide or lithium hydroxide and this component may be present in amounts from about 0.2 wt. % up to about 20 wt. %, the preferred range being about 4 wt. % to 10 wt. %. NaOH is preferred as the second component catalyst.
• the process of this invention is also applicable to the reaction of mixed alcohols to form the corresponding mixed esters.
• a branched C16 alcohol may be reacted with 2-ethylhexanol and there will be formed a C16 ester, a C24 ester and a C32 ester.
• the invention is illustrated by the following examples which are not to be considered as limitative of its scope.
• the platinum/carbon catalyst used in all examples was 5 wt. % platinum dispersed onto activated carbon powder having a surface area of 1200 M2/g. and a mean particle size of 30 microns with 90% of the powder having a particle size less than 70 microns.
• the solution was cooled to ambient temperature and 0.24 g. of 5% platinum on carbon powder was added.
• the solution was again heated to reflux. After 20 minutes the temperature of the refluxing solution had risen to 190°C. Thereafter the pressure was gradually reduced as needed to maintain a solution temperature of 190°C.
• Example 1 The procedure of Example 1 was used. Sodium hydroxide, 9.64 g. was used as the base. The reaction temperature was 195°C and the time of heating was 4 hours.
• Example 1 The general procedure of Example 1 was used. The amount of NaOH was 3.8 gms., the amount of 5% Pt/C was 0.12 g., the reaction temperature was 181°C-183°C and the reaction time was 2 hours, analysis showed 7% conversion to the ester.
• Example 1 The general procedure of Example 1 was used. The amount of NaOH was 7.6 gms., the amount of 5% Pt/C was 0.36 gms., the reaction temperature was 178°C-185°C and the reaction time was 2 hours.
• the stirred mixture was heated to 190°C for 4 hours, while passing nitrogen through the solution to remove any water formed, as well as the hydrogen produced during reaction.
• Zinc stearate (2.0 g.) was added and refluxing continued for 4.5 additional hours, during which time the temperature rose to 195°C.
• the hazy solution was cooled and washed twice with aqueous acetic acid. The conversion to C16 ester was 51%.
• Example 5 The procedure of Example 5 was followed with 121.3 g. (0.5 mole) of the branched C16 alcohol, 65.1 g. (0.5 mole) of 2-ethylhexanol as reactants with 10 g. KOH and 2.0 g. ZnO as catalyst. The heating at 190°C was continued for 4 hours. The cooled and washed product analysis showed it to contain 14.0% unreacted 2-ethylhexanol, 33% unreacted C16 alcohol, 14% C16 ester, 25.6% mixed C24 ester and 12,4% C32 ester. This experiment shows that the inven­tion is applicable to mixed alcohol reactants.
• Example 1 The procedure of Example 1 was followed.
• the amount of NaOH was 0.91 gm.
• the amount of 5% Pt/C was 0.240 gm.
• the reaction temperature was 181°C-186°C, and the reaction time was 3 hours. Analysis of the washed product indicated 28% conversion to ester.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)

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• 1988
  • 1988-07-08 CA CA000571595A patent/CA1321209C/en not_active Expired - Fee Related
  • 1988-07-19 EP EP88306605A patent/EP0300738B1/de not_active Expired - Lifetime
  • 1988-07-19 AT AT88306605T patent/ATE97399T1/de active
  • 1988-07-20 JP JP63181443A patent/JPS6463551A/ja active Pending

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